Within the field of watch-making, a conventional architecture is used to make movements, which are provided with striking mechanisms, such as alarms or minute repeaters. In such embodiments, the gong or gongs used are each formed by a metal wire, which is generally circular in shape and placed in a parallel plane to the watch dial. The metal wire of each gong is generally arranged around the movement, in the watch frame and above a plate on which the various parts of the movement are mounted. One end or several ends of each gong are fixed, for example by soldering, to a gong-carrier integral with the plate, for example, which may be common to all of the gongs. The other end of each gong may generally be free.
The watch striking mechanism includes at least one hammer actuated at predetermined times. The vibration of each gong is generated by the impact of the corresponding hammer on the gong, in particular, in proximity to the gong-carrier. Each hammer makes a partial rotation in the plane of the gong(s) so as to strike the corresponding gong and cause it to vibrate in its plane. Part of the gong vibration is also transmitted to the plate by the gong-carrier.
The mechanical impact between the hammer and the gong of a conventional striking mechanism is difficult to control. The same is true for optimization of acoustic efficiency, which is greatly limited within the audible frequency range, particularly within the range of frequencies between 1 kHz and 4 kHz, but also between 4 kHz and 20 kHz. This is due to the fact that the mechanical impact of the hammer against the gong is of very short duration and most of the energy is transmitted at high frequency vibration modes above 4 kHz. The duration of impact of the hammer against the gong generally cannot be increased by altering the geometry, inertia and material of the parts involved, without also causing a marked decrease in the impact energy. Further, mechanical shocks, particularly the impacts of the hammer against the gong, may cause spurious noise, especially in the case of double impact, and lead to wear of gong, which is a drawback.
EP Patent No. 2 048 548, which mainly discloses a hammer for a watch striking mechanism, may be cited in this regard. This hammer includes two parts hinged to each other and a resilient member secured to one of the hinged parts. When the hammer is in a stable position, the resilient spring member holds the two parts of the hammer, whereas when the hammer is in the striking position, the two parts move away from each other, returned by the resilient spring member. This hammer arrangement complicates the making of a striking mechanism, which is a drawback. Further, any mechanical impact of the hammer may also cause spurious noise, which is another drawback.
FR Patent Nos. 2 407 862 and 1 214 428 disclose a striking device for a clock. This striking device includes, in particular, a rotatably mounted hammer, driven by means of an electro-magnet in the direction of a bell, to generate a sound during the mechanical impact of the hammer against the bell. As mentioned hereinbefore, any mechanical impact of the hammer against the bell may also cause spurious noise, which is a drawback.